Title

Metastable hydrated carbonates for algae biofuel production

Conference Dates

May 22-26, 2017

Abstract

In this work, we present a study to develop a mineralization process to capture and reuse carbon dioxide (CO2) for the growth of algae, from which then carbon is extracted and converted into a biofuel. The classical CO2 mineralization process consists in fixing CO2 into stable carbonates. During the formation of the carbonates hydrated phases can form, which transform into stable carbonates, eventually. However, if carbonates are designed to be reused, e.g., to provide carbon to a bioprocess through dissolution within a brine, the formation of metastable carbonate phases is preferred as these phases have a solubility which is much higher than the solubility of the anhydrous phases. To design a process that can capture CO2 into hydrated minerals and provide carbon for algal growth, meeting the requirements of the synthesis of the carbon into fatty acids, requires a well-constrained mineralization. In particular, optimal thermodynamic conditions for precipitation and dissolution must be selected. Here, we present an experimental and modeling study of the precipitation and the dissolution of nesquehonite (MgCO3·3H2O). We investigated the process between 25ºC and 50ºC and 1 and 5 bar of CO2. Batch experiments were performed using MgCl2-CO2-Na2CO3 aqueous system and monitored with online Raman spectroscopy. Precipitation and dissolution were modeled using a population balance equation (PBE) coupled with a geochemical model. Nucleation, growth, and dissolution rates were described by constitutive equations based on classical nucleation theory, the birth-and spread growth mechanism, and transition state theory, respectively. The kinetic parameters were estimated by fitting Raman spectroscopy measurements using multivariate kinetics modeling.

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